Synthetic auxins are used to get rid of dicot, such as Dandlions and thistles in areas reserved for monocots such as grain fields. A dicot responds to unnaturally high concentrations of auxins by growing rapidly and then die; whereas monocot, remains unaffected by the treatment.
Auxins are of two types :
(1) Natural auxins : These are naturally occuring auxins, isolated from plants and are regarded as phytohormones e.g. IAA. NAA etc.
(2) Synthetic auxins : These are synthesized by artificially e.g. IBA 2,4-D etc.
Auxin was isolated by F.W. Went from tips of coleoptiles of oat seedling.